The present invention relates to a method of manufacturing a part in a connector or a device for an optical fiber, which part is disposed at the center of the connector or of the device to hold the optical fiber and is called a ferrule.
Conventionally, a ferrule is in the form, for example, as shown in FIGS. 1(a)-1(d), and is usually formed of zirconia ceramics.
FIGS. 1(a) and 1(b) show a single-core type ferrule 1. To take an actual product for instance, it has a columnar shape having a diameter of around 2 mm and a length of around 8 mm and also has in the center a perfectly circular hole 2 with a diameter of around 0.125 mm. FIGS. 1(c) and 1(d) show a two-core type ferrule, and actual products are of like dimensions.
Meanwhile, Japanese Patent Application No. 375372/1998 filed by the inventors of the present invention proposes a metallic ferrule manufactured using a metal such as nickel by a method in which the metal is subjected to electrocasting using one or more metallic or plastic wires as mother dies, followed by machining of the resulting electrocast product after removal of the wire or wires.
According to the above patent, electrocasting is implemented in an apparatus, for example, as shown schematically in FIG. 2. More specifically, the apparatus is composed essentially of an electrocasting solution 3, positive electrodes 4, a holding jig 5, an air agitating nozzle 6, a spring 7, a negative electrode 8, and a length of wire 9, as shown in FIG. 2.
In the proposed method, four positive electrodes 4, each having nickel balls contained in a cylindrical titanium basket, are placed in the electrocasting solution 3 based on a warmed nickel sulfamate or the like and are arranged in the four corners of a tank 10 of the solution 3 to surround the holding jig 5. The holding jig 5, which is set in the center, is provided with the negative electrode 8. The wire 9, such as a stainless wire, is fixed to the electrode 8 and is maintained under tension by the spring 7. A direct current is sent across the electrodes to carry out electrocasting under feeding of a small amount of air through the air agitating nozzle 6. However, this method involves the following problem.
Variation in current-carrying properties at contacts of the positive electrodes 4 disposed in the four corners and cavities formed by local plugging with the nickel balls in the positive electrodes 4 are mainly causative of biased wall thickness in the electrocast part, frequently. This, in turn, causes decentering of the hole.
Further, if biased thickening occurs in the electrocast portion, the resulting rod-shaped electrocast product fails to have a perfectly circular cross section, causing difficulty in machining which follows as after-processing.
Moreover, biased thickening in the electrocast portion induces an internal stress that frequently leads to bending in the resulting electrocast product. This can cause decentering of the hole at the time of subsequent machining or can make the product unprocessable.
When a hole is to be defined in a ferrule, an extremely strict center hole accuracy is generally demanded (permissible decentering: about xc2x10.5 xcexcm). This involves significant problems in the quality and the cost in that occurrence of decentering of a hole in the electrocasting process can make centering and machining of the resulting product extremely troublesome in after-processing. An excessive degree of decentering of a hole, if occurred, will make centering and machining impossible. Meanwhile, the failure in obtaining a perfectly circular cross-section additionally requires an extra prefinishing treatment by means of lathing.
In addition, since the electrocasting solution is agitated mainly by air agitation, the atmosphere in the workshop tends to be extremely humid. Since the humidity is of acidic, there have been problems that it is likely to cause troubles in the equipments used and that it deteriorates the work environment for operators.
Further, a single rectifier generally sends electricity to about 10 to 30 holding jigs 5 in manufacture, so that current-carrying properties differ greatly among the holding jigs due to corrosion at the contacts thereof, resulting in great variation in the thickness (diameter) among the finished electrocast products. Meanwhile, since the thickness of the thinnest electrocast product held on a holding jig must be increased to a predetermined diameter, this causes waste in the electrocasting time and waste of the electrocasting metal and makes machining as after-processing troublesome or difficult.
In view of the above, it is an object of the present invention to provide a method of manufacturing a ferrule in which at least one wire of metal or the like is used as a mother die to effect electrocasting and then the resulting electrocast product is machined after removal of the wire. More specifically, it is an object of the present invention, in the above method, to notably improve quality and productivity of ferrules and to reduce on a wide margin the cost of manufacturing them by implementing electrocasting without causing biasing in the wall thickness nor bending to readily meet the extremely strict center hole accuracy (permissible decentering degree: xc2x10.5 xcexcm) and obtain an intermediate rod product having a perfectly circular cross section after the electrocasting treatment, by dispensing with the specific air agitation causative of various troubles and by reducing variation in the diameter among the products so as to save labor in machining as after-processing on a wide margin.
In order to attain the above-mentioned object, the present invention employs a method of carrying out electrocasting against wires under rotation thereof, while they are maintained static in the longitudinal directions to prevent biasing in the wall thickness of each electrocast product, as well as, bending and variation in the cross-sectional roundness thereof. The method of the present invention employs, in place of air agitation or the like, moving of the wires and the electrocasting solution, as necessary, to correct variation in the diameter among the products by making use of an ampere hour meter, for example, where leading current is stopped automatically at the stage that the ampere hour meter, reading the current for electrocasting, designates an appointed value.